I'm in the process of installing a footing drain with perforated PVC pipe (not the corrugated pipe). Do I place the pre-drilled holes in the 10 o'clock/2 o'clock position (closer to the surface), or the 5 o'clock/7o'clock position (away from the surface)? Also, I realize that gravel should surround the full length of the pipe. But what about the felt wrapping? Do I encircle the pipe with the fabric along its entire length?
The short answer is to install the pipe so its parallel rows of holes are in the 5 o’clock/7 o’clock position. And yes, you should completely encircle both the drain line and a layer of stone with filter fabric.
But, as the saying goes, the devil is in the details. The key is installing these components so they prevent the accumulation of fine silt in the drain lines.
Done correctly, a perimeter drain is great insurance against a water-logged furnace, ruined golf clubs and all the other unpleasant surprises that come with a wet basement.
Although adding the drains in a retrofit is always possible, it’s a lot more expensive and disruptive than installing them before the foundation is backfilled.
Protect drain line with crushed rock and fabric
PVC pipe used for foundation drain is typically 4 in. in diameter. Rigid pipe is less susceptible to problems than the flexible variety which uses a series of slits rather than round holes to gather water.
Filter fabric, a kind of textile that can be used below grade, and 3/4-in. stone are used in tandem to keep the silt out of your drains. Here’s how to layer them:
Once you’ve cleaned out a trench along the foundation footing, line it with a continuous length of filter fabric 6 ft. wide. Now add a bed of 3/4-in. rock 3 in. deep and 1 ft. wide.
Next comes the perforated PVC, then another layer of stone at least 6 in. deep.
Finally, overlap the edges of the filter fabric to create a protective sheath around the PVC and stone.
Some foundation specialists also recommend a layer of coarse sand over the filter fabric as a secondary line of defense against silt.
You won’t be able to get much of a pitch on the perforated pipe, but make sure the outlet pipe carrying water away from the foundation is sloped at least 1/4 in. per foot.
That’s not all you can do
If you have yet to pour your basement floor, think about installing a perimeter drain on the inside of the foundation as well. It’s an excellent way of capturing water that sneaks past the exterior drain.
There are several kinds of interior drains. No matter what type you choose, it’s designed to carry ground water to a plastic sump liner. There, a pump kicks on when enough water has accumulated and gets it out of the house.
Beyond installing interior and exterior drain systems there are two other products you might consider:
- A waterproof coating on the outside foundation walls instead of the less expensive and less effective damp-proofing that budget-minded builders often recommend. The rubber-like coating is sprayed on to form a flexible barrier against water infiltration.
- A layer of high-density polyethylene sheeting beneath the basement slab. That will prevent ground water from being pushed upward.
Taking these steps isn’t cheap -- no argument there.
But consider how much more expensive it will be when a lesser system fails. And that’s to say nothing of that prized bed of azaleas that will have to go when the contractor digs in with a backhoe.
